An Ocean Thermal Energy Conversion (OTEC) system utilizes the differential between the relatively warm upper surfaces of the ocean in the waters around the earth's equator and the colder waters at depths of around 1,000 meters. In a closed OTEC system, a working fluid of relatively low boiling point, such as ammonia, is vaporized in a first heat exchanger section of the system by the warm ocean water. That vaporized working fluid turns a turbine to generate electricity, and the working fluid vapor is then condensed in a second heat exchanger section using the colder ocean water that is pumped from the depth of around 1,000 meters.
A problem with current OTEC systems is that they are not very efficient, and much of the electrical energy produced by the system is needed to run the pumps that pump the cold ocean water up to the heat exchanger that condenses the working fluid.